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The Baltic Sea ecosystem

The Baltic Sea ecosystem

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Which of the following statements about the average salinity of the Baltic Sea is true?

The Baltic Sea ecosystem

Last year Lina and Leon spent summer by the Baltic Sea. This year they are on holiday by the Mediterranean Sea. Leon runs into the water, splashing like mad, as he did last year in the Baltic. But a second later, he runs back, spitting and rubbing his eyes. Ugh, this water is so much saltier than the Baltic Sea!

This was a slightly painful way to discover that the Baltic has a lower salt concentration than other seas. The Baltic sea is located in the North of Europe, bordered by the Scandinavian peninsula and continental Europe. The Baltic Sea connects to the Atlantic Ocean only through the North Sea and several shallow straits. More than two hundred rivers flow into the Baltic from the surrounding land. The rivers supply water from an area four times the size of the sea itself!

All these rivers bring plenty of freshwater into the Baltic, so the concentration of salt in the seawater decreases. The Baltic Sea is shallow, and the straits that connect it to the Atlantic ocean are narrow, so the waters from the two don't mix very well. Because the climate here is cool, not much water evaporates. So, the concentration of salt - salinity - is kept low. While the average salinity of the oceans is about 3.5 percent, that of the Baltic Sea is on average only about 0.8 percent.

This makes water in the Baltic neither fresh nor salty - what we call brackish. The western Baltic, closer to the straits, has higher salinity, as much as 2.5 percent. Salinity in the northern Baltic is as little as 0.1 percent. Conditions in the shallow, brackish waters of the Baltic Sea are not suitable for all organisms. There is no great variety of plants and animals here.

However, there might be many of the same kind, or species. Both freshwater species and saltwater, marine, species can be found in the Baltic Sea. These include algae, plants, animals, and even bacteria. Most of the marine fish species, such as cod, herring, hake, or flounder, live in the west of the Baltic. As salinity decreases, closer to the coast and in the northern Baltic, there are fewer marine species and more freshwater species.

These include for example perch, pike, or roach. The Baltic Sea is also home to many marine mammals, such as the harbour porpoise, grey seal, as well as many waterbirds, for example, the herring gull. All these living and non-living elements create a unique ecosystem. The characteristics of the Baltic Sea make this ecosystem very vulnerable and sensitive to change. There are many major cities located along the Baltic coast and large areas of land used for farming and industry.

So, chemicals and other pollutants from these areas sooner or later end up in the Baltic. These cause water pollution and increase the amount of nutrients in the water. This can lead to increased growth of algae and some types of bacteria, which can be dangerous to other species in the sea, and even to humans. Sea traffic and the fishing industry have a huge impact on the ecosystem too. Human activities contribute to pollution and affect organisms, salinity, and levels of oxygen in the Baltic Sea.

It takes about thirty years for the water in the Baltic to renew. So the Baltic ecosystem can still recover, if given a chance. And that would benefit both us and nature.